The present invention relates to a liquid ejecting method, a liquid ejecting head, and a liquid ejecting apparatus, which record an image on a piece of recording medium by ejecting liquid in the form of a droplet so that the liquid adheres to the recording medium.
A liquid ejecting recording method for recording an image by adhering liquid to a piece of recording medium by ejecting liquid in the form of a droplet from an ejection orifice with the use of thermal energy is superior to the other recording methods in that it can record a high quality image, it can record in high resolution, it can record at a high speed, it can record with low noise, it can easily record in color, and it can record on ordinary paper.
In order to produce a high quality image with the use of a liquid ejecting recording method, it is necessary to stabilize the volume by which liquid is ejected in the form of a droplet. Therefore, a liquid ejecting recording method has been devised in various ways. For example, according to the method proposed in Japanese Laid-Open Patent Application No. 10941 or the like, a bubble is generated in the liquid in a liquid path leading to an ejection orifice, with the use of thermal energy, and the liquid in the liquid path is ejected from the ejection orifice while allowing the bubble to open into the atmosphere under a condition that the linear differential value of the velocity, at which the leading end of the bubble in terms of the direction in which the bubble is ejected, is negative. In a liquid ejecting head which employs this method, the distance from the heater for generating thermal energy to an ejection orifice is relatively short. Therefore, a liquid ejecting head which employs this method is better than the prior liquid ejecting head in terms of the ratio of the electrical energy given to the heater relative to the amount of work accomplished by the bubble. In other words, this liquid ejecting method is superior to the prior liquid ejecting methods in terms of energy efficiency. Further, in the case of this method, the liquid present between the heater and the ejection orifice is almost entirely ejected, which makes this method superior to the prior methods in terms of the uniformity of the volume by which liquid is ejected each time.
However, there was much to be improved in the conventional liquid ejecting technology such as the one described above. For example, the conventional technologies can reduce the amount of splashing or misting of the liquid, by ejecting the liquid droplet while allowing a bubble to open into the atmosphere under the condition that the linear differential value of the velocity of the leading end of the bubble in terms of the liquid ejecting direction is negative. In other words, the conventional technologies can prevent image quality from being reduced by the splashing or misting of the liquid. However, the conventional technologies leave much to be desired in terms of the amount by which they reduce the image quality degradation by preventing the splashing or misting of the liquid.
Further, in the case of the conventional liquid ejecting method, at the time of liquid ejection, a small column of liquid is formed for an extremely short period of time at the center portion of an ejection orifice, and the point at which a bubble becomes connected to, or integrated with, the atmosphere is mostly adjacent to this column of liquid. In other words, a bubble comes in communication with, or becomes integrated with, the atmosphere at a point away from the center of the ejection orifice. As a result, the trailing end of a bubble does not align with the center of the ejection orifice. This affects the direction in which the liquid droplet flies, affecting thereby the accuracy with which the liquid droplet lands on the target point on the recording medium. Also in terms of this aspect of liquid ejection, the conventional technologies must be greatly improved to keep recording quality at a high level.
As described above, preventing liquid from being splashed or misted, and also improving the accuracy with which each liquid droplet lands on the target point on recording medium, so that recording quality is further improved, are extremely important objects for a liquid ejection method.
The primary object of the present invention is to provide a liquid ejecting method, a liquid ejecting head, and a liquid ejecting apparatus, which are stable in terms of the volume by which liquid is ejected each time, the velocity at which liquid is ejected, and the point on which the liquid lands.
Another object of the present invention is to provide a liquid ejecting method, a liquid ejection head, and a liquid ejecting apparatus, which can prevent the ejected liquid droplet from splashing or misting.
Another object of the present invention is to provide a liquid ejecting method, a liquid ejecting head, and a liquid ejecting apparatus, which make it possible to record at a high level of recording quality.
Another object of the present invention is to provide a liquid ejecting method which ejects liquid in the form of a droplet by forming a bubble in the liquid on a heat generating member with the use of thermal energy generated by the heating member provided on a piece of substrate, and which comprises a process in which a bubble deforms in such a manner that the center portion of the bubble wall, or the interface between the liquid and vapor, in other words, the bubble wall portion on the side opposite to the substrate, makes contact with the substrate, and a process in which the bubble opens into the atmosphere, at its periphery, at the same time, or after, the contact between the aforementioned center portion of the bubble wall and the substrate.
Another object of the present invention is to provide a liquid ejecting head which comprises a plurality of ejection orifices through which liquid is ejected in the form of a droplet, a plurality of liquid paths leading to the plurality of liquid ejection orifices, one for one, a plurality of heat generating members faced, one for one, toward the plurality of liquid ejection orifices to generate the thermal energy used for forming bubbles so that liquid is ejected from the plurality of liquid ejection orifices, a piece of substrate on which the plurality of heating members are disposed, and in which a bubble deforms in such a manner that the center portion of the bubble wall makes contact with the substrate, and a process in which the bubble opens into the atmosphere, at its periphery, at the same time, or after, the contact between the center portion of the bubble wall and the substrate, and also to provide a liquid ejecting apparatus which comprises such a liquid ejecting head.
According to the present invention, the trailing end portion of the column of liquid, that is, a portion of the interface between the vapor portion (bubble) and the liquid, almost perfectly aligns with the central axis of the corresponding ejection orifice, at the same time as, or preferably before, the bubble opens into the atmosphere. The column of liquid flies away from the ejection orifice, following substantially the central axial line of the ejection orifice, with the trailing end of the column of liquid remaining in contact with the surface the corresponding substrate until the distance between the leading end of the column of liquid and the surface of the substrate becomes substantial. Therefore, the column of liquid remains straight, and flies away straight in the form of a droplet after it becomes separated from the substrate surface.
Further, according to the present invention, a bubble, or the vapor portion, becomes connected to the atmosphere, in the liquid path, adjacent to the substrate, at the same time as, or preferably immediately before, the column of liquid becomes a liquid droplet, that is, at the same time, or preferably immediately before, the trailing end of the column of liquid is separated from the liquid in the liquid path, in the ejection orifice, adjacent to the substrate surface. Therefore, the liquid is prevented from splashing or misting, and should the splashing or misting of the liquid ever occur, the splashed or misted liquid is prevented from being ejected out of the liquid path. Further, the liquid is ejected by a constant volume, at a constant velocity, and the trailing end of the liquid droplet, that is, the trailing end of the column of liquid, always behaves the same. Therefore, image quality is not derogatorily affected by satellite liquid droplets. As a result, a high quality image can be recorded.
Further, according to the present invention, a bubble opens into the atmosphere. In other words, the process in which a bubble shrinks and perishes does not exist. Therefore, the heaters are prevented from being damaged by cavitation. As a result, a liquid ejecting head lasts longer.